Igniter assembly for rocket motors

ABSTRACT

1. In a rocket motor having a combustion chamber, a receptacle in said combustion chamber, an igniter assembly received by said receptacle, said igniter assembly including at least two spaced containing means one interior of the other, the interior one of said containing means being perforate and the exterior one thereof being imperforate, igniter charge means disposed between said spaced containing means, means dividing the interior one of said containing means into an inner end and an outer end, said inner end communicating with said combustion chamber, booster charge means received in said outer end, adaptor means enclosing said igniter assembly in said receptacle, said adaptor means including initiator charge means communicating with said booster charge means, and a squib for igniting said initiator charge means so that upon ignition said squib will, in order, cause initiation of said initiator charge means, said booster charge means, and said igniter charge means causing a detonation wave to pass through said inner end into said combustion chamber.

United States Patent 1191 Boydston 1 51 Sept. 23, 1975 IGNITER ASSEMBLY FOR ROCKET MOTORS [75] Inventor: William M. Boydston, Newport Beach, Calif.

[73] Assignee: Aerojet-General Corporation, El

Monte, Calif.

22 Filed: Jan. 7, 1965 21 App]. No.: 424,141

Primary ExaminerRobert F. Stahl Attorney, Agent, or Firm-Edward O. Ansell EXEMPLARY CLAIM 1. In a rocket motor having a combustion chamber, a receptacle in said combustion chamber, an igniter assembly received by said receptacle, said igniter assembly including at least two spaced containing means one interior of the other, the interior one of said containing means being perforate and the exterior one thereof being imperforate, igniter charge means disposed-between said spaced containing means, means dividing the interior one of said containing means into an inner end and an outer end, said inner end communicating with said combustion chamber, booster charge means received in said outer end, adaptor means enclosing said igniter assembly in said receptacle, said adaptor means including initiator charge means communicating with said booster charge means, and a squib for igniting said initiator charge means so that upon ignition said squib will, in order, cause initiation of said initiator charge means, said booster charge means, and said igniter charge means causing a detonation wave to pass through said inner end into said combustion chamber.

5 Claims, 2 Drawing Figures US atent Sept 23.1 75

INVENTOR. WILLIAM M. BOYDSTON BY 96mg M ATTORNEY IGNITER ASSEMBLY FOR ROCKET MOTORS This invention generally relates to igniters, and more particularly to a novel enclosed igniter assembly of unitary construction for insertion into a receptacle such as a tubular guide member which is fixed to a wall of a combustion chamber in a rocket motor and extends within the chamber, the igniter assembly being so constructed as to provide for uniform combustion of the igniter charge contained therein.

In the field of rocket motor ignition where a solid porpellant grain propellant utilized, it is the general practice to employ a two-piece igniter comprising a pyrotechnic material and an initiator for the pyrotechnic material. The initiator is removably disposed within thecombustion chamber of the rocket motor, while the pyrotechnic material is permanently installed within the combustion chamber adjacent the solid propellant. This type of two-piece igniter typically tends to produce an initial early and excessive surge of pressure in the combustion chamber to create, in part, overpressure or ovenpeak, which is caused by uneven and non-instantaneous application of the combustion products from the pyrotechnic material of the igniter to the solid propellant. This over-pressure requires a stronger combustion chamber if the rocket motor is to be able to operate without failure, and the necessary added strength of the combustion chamber is invariably obtained only by increasing the weight of the part of the rocket motor comprising the combustion chamber. The early surges of pressure in the combustion chamber also cause uneven application of impulse and potentially excessive acceleration loads to the rocket motor. Furthermore, the pyrotechnic material was contained in receptacles readily subject to disintegration by heat erosion into particles which would be carried into the combustion chamber to adversely affect the burning of the solid propellant. A two-piece ignition system of the type described also raises certain difficulties in the application of maximum safety practices or surveillance inspection of the igniter assembly when installed in place in the rocket motor because the combustion chamber is required to be completely removed from the remainder of the rocket motor in order to gain proper access to the pyrotechnic material of the igniter assembly which is permanently fixed within the combustion chamber.

It is therefore, an object of this invention to provide an improved igniter assembly of unitary construction which is easily installed in a combustion chamber of a rocket motor and may be readily removed therefrom.

It is another object of this invention to provide an improved igniter assembly capable of generating rapid and substantially uniform ignition of a solid propellant.

It is a further object of this invention to provide an igniter assembly so constructed as to cooperate with a tubular guide member which is fixed to a wall of the combustion chamber and extends therewithin, wherein the combustion products of the ignition charge are directed into, and controlled within, the combustion chamber containing a solid propellant.

It is further an object of this invention to provide an improved igniter assembly, wherein the burning rate of the ignition charge of the igniter assembly is itself controlled and the ignition charge is retained with the remainder of the igniter assembly after the ignition charge has been consumed.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds when taken in connection with the accompanying drawings in which FIG. 1 is fragmentary sectional view of a combustion chamber for a rocket motor having a solid propellant grain therein, with the novel igniter assembly according to the present invention being installed in the combus tion chamber the igniter assembly being partially shown in elevation and broken away for purposes of clarity; and

FIG. 2 is a longitudinal sectional view of the igniter assembly.

Referring more specifically to the drawings, a tubular cylindrical guide member 12 is secured to a wall of a combustion chamber 14 of a rocket motor, the tubular guide member 12 extending within the combustion chamber 14 and having a radially outwardly projecting threaded annular flange 15 on the outwardly disposed end thereof threadably engaged by the wall of the combustion chamber 14. The wall of the combustion cham ber 14 is suitably apertured to provide for insertion of the tubular guide member 12 within the combustion chamber 14. A set screw 16 extends transversely through a portion of the wall of the combustion chamber 14 into the radial flange 15 to secure the tubular guide member 12 in place and prevent inadvertent loosening of the threaded connection between the tubular guide member 12, and the wall of the combustion chamber 14. The combustion chamber 14 contains a solid propellant grain 17 fixed therein and disposed in proximity to the inner end of the tubular guide member 12. The tubular guide member 12 is provided with a closure wall 20 at the inner end thereof. A deflector block 22 of suitable material, such as heat-resistant plastic, is disposed within the tubular guide member 12 in engagement with the closure wall 20 at the inner end thereof. The deflector block 22 has an off-set bore 24 extending therethrough, the off-set bore 24 comprising an axially extending bore portion at the end of the block 22 remote from the closure wall 20 and an angular bore portion extending radially outwardly at an incline from the axially extending bore portion. The angular bore portion of the off-set bore 24 is alined with an opening 26 formed in the tubular guide member 12 adjacent the inner end thereof to provide communication between the interiors of the tubular guide member 12 and the combustion chamber 14. The off-set bore 24 in the deflector block 22 includes the angular bore portion for properly orienting the bore 24 to the solid propellant grain 17. It will be understood that the bore 24 may be formed so as to have any suitable configuration capable of achieving proper orientation with the solid propellant grain 17.

The outer end of the tubular guide member 12 is open, as at 28, for receiving an igniter assembly 30 therein. The igniter assembly 30, as best shown in FIG. 2, comprises an outer imperforate cylindrical tube 32 and an inner concentric perforate cylindrical tube 34 disposed in radially inwardly spaced relation to the outer tube 32 to provide an annular space 36 therebetween. The outwardly disposed ends of the tubes 32, 34 are respectively secured to an adaptor or fitting 38 by suitable means, such as welds 39. The outer tube 32 is provided with an integral radially inwardly directed flange 40 at its other end, the flange 40 extending into engagement with the inner tube 34 and forming a closure at the inner end of the annular space 36 between the tubes 32, 34. The inner tube 34 is provided with a plurality of apertures or openings 42 which are substantially uniformly distributed over the inner tube 34. Within the annular space 36 between the outer and inner tubes 32, 34, an igniter charge 44 is disposed. The igniter charge 44 preferably comprises a plurality of pyrotechnic pellets 45 positioned in longitudinal rows, with the rows of pyrotechnic pellets 45 being arranged in juxtaposed relation to substantially fill the annular space 36. Annular gaskets 46 may be positioned at each end of the annular space 36 in respective engage ment with the outer and inner tubes 32, 34, the annular gaskets 46 being made of suitable resilient material and serving as a buffer or cushion for each end of the igniter charge 44 comprising the pyrotechnic pellets 45.

The inwardly disposed end 48 of the inner tube 34 is open, while the outwardly disposed end 50 of the inner tube 34 is received by a central hub or mouth 52 provided on the adaptor 38 to which it is secured as previously indicated by weld 39. A booster charge 54 comprising a plurality of small tablets or cakes is received in the inner tube 34, the booster charge 54 being positioned in the portion thereof adjacent the outwardly disposed end 50 of the inner tube 34. A wad 56 is provided in the inner tube 34 medially of the ends thereof, the wad 56 being positioned in abutment with the booster charge 54 to confine the booster charge 54 between the wad 56 and the hub or mouth 52 of the adaptor 38.

The adaptor 38 is provided with a central bore 58 which extends through the hub or mouth 52 thereof, the bore 58 connecting into a cavity or chamber 59 containing a primary initiation charge 60 comprising a plurality of small tablets or cakes of suitable pyrotechnic relay materials. The adaptor 38 is further provided with a pair of threaded axial ports opening onto the outer end surface of the adaptor 38 and communicating with the cavity 59 in which the tablets comprising the primary initiation charge 60 are contained. One of the axial ports in the adaptor 38 may be used to introduce the tablets comprising the primary initiation charge 60 into the cavity 59, and is normally closed by a threaded plug 61 following the filling of the cavity 59 with the primary initiation charge 60. The other axial port in the adaptor 38 receives a threaded squib 64 to which a pair of electrical conductors or wires 66 are secured, the wires 66 extending outwardly of the adaptor 38 to a suitable source of controlled electric energy. Upon supplying electric energy to the squib 64, it is actuated to cause the primary initiation charge 60 to be ignited.

In use, the tubular guide member 12 is threadably secured to a wall of the combustion chamber 14 by its radially outwardly projecting flange so as to extend within the combustion chamber 14. The tubular guide member 12 is oriented by appropriately positioning the opening 26 adjacent the inner end thereof with respect to the solid propellant grain 17. When it is desired to fire the rocket motor, the unitary igniter assembly is inserted into the tubular guide member 12 and secured to the wall of the combustion chamber 14 by threading the adaptor 38 in place. No particular orientation between the igniter assembly and the guide assembly comprising the tubular guide member 12 and the deflector block 22 with the off-set bore 24 is required. Upon actuation of the squib 64 to ignite the primary initiation charge 60, the resultant detonation wave passes through bore 58 and ignites the booster charge 54. The ignition of the booster charge 54 in turn causes the ignition of the pyrotechnic pellets 45 by creating a detonation wave passing through the openings 42 in the inner tube 34 disposed in the portion thereof adjacent the outwardly disposed end 50 of the inner tube 34. The amount and configuration of the booster charge 54 in combination with the retention strength of the wad 56 provide an effective control of the initiation rate of the initiator charge 44. The ignition of the igniter charge 44 comprising the pyrotechnic pellets 45 sets up a further detonation wave which passes radially inwardly through the openings 42 and into the inner tube 34 from where the detonation wave passes through the open end 48 of the inner tube 34 into the off-set bore 24 of the deflector block 22. The detonation wave is then directed by the off-set bore 24 through the opening 26 in the tubular guide member 12 against the solid propellant grain 17 disposed in the combustion chamber 14.

There has been disclosed a unitary igniter assembly for a rocket motor having a solid propellant grain disposed in the combustion chamber thereof. The detonation wave caused by the ignition of the pyrotechnic pellets 45 of the igniter assembly is emitted from the opening 26 of the tubular guide member 12 in a jet pattern, and a high percentage of the energy from the latter detonation wave is directly applied to the solid propellant grain 17 to significantly reduce the amount of overpressure which characteristically occurs during the ignition of certain solid propellant grains. In using the improved igniter assembly, preheating of the grain surfaces of the solid propellant prior to the complete ignition thereof is substantially avoided to insure that the propellant grain is properly ignited and burns at its normal expected rate of burning.

While the foregoing is a description of a preferred embodiment of the invention, the following claims are intended to include those modifications and variations that are within the spirit and scope of the invention.

1 claim:

1. In a rocket motor having a combustion chamber, a receptacle in said combustion chamber, an igniter assembly received by said receptacle, said igniter assembly including at least two spaced containing means one interior of the other, the interior one of said containing means being perforate and the exterior one thereof being imperforate, igniter charge means disposed between said spaced containing means, means dividing the interior one of said containing means into an inner end and an outer end, said inner end communicating with said combustion chamber. booster charge means received in said outer end, adaptor means enclosing said igniter assembly in said receptacle, said adaptor means including initiator charge means communicating with said booster charge means, and a squib for igniting said initiator charge means so that upon ignition said squib will, in order, cause initiation of said initiator charge means, said booster charge means, and said igniter charge means causing a detonation wave to pass through said inner end into said combustion chamber.

2. In a rocket motor as defined in claim 1, wherein said receptacle includes deflector means attached to said inner end of the interior one of said containing means for selectively directing said detonation wave into said combustion chamber.

3. In a rocket motor as defined in claim 1, wherein the strength of said interior dividing means may be varied, in conjunction with variation in the shape and amount of said booster charge means, to provide control of the initiation rate of said igniter charge means.

4. An igniter assembly for rocket motors, said igniter assembly comprising inner and outer concentric elongated tubes disposed in radially spaced relation to each other to define an elongated longitudinally extending annular space therebetween, an igniter charge disposed in the annular space between said inner and outer tubes, said inner tube having a plurality of apertures therethrough providing communication between the annular space and the interior of said inner tube, means defining a partition within said inner tube dividing the interior of said inner tube into inner and outer portions, a booster charge disposed in the outer portion of said inner tube, and means for initiating the ignition of said booster charge, and the ignition of said booster charge causing ignition of said igniter charge along the length of the annular space such that a detonation wave passes through apertures in said inner tube into the inner portion thereof and outwardly through the inner end of said inner tube.

5. An igniter assembly as defined in claim 4, further including a tubular guide member having a closed inner end and provided with a deflector block received therein at the closed inner end thereof, said deflector block having an off-set bore extending therethrough which comprises an axially extending bore portion communicating with the interior of said tubular guide member and an angular bore portion extending radially outwardly from the axially extending bore portion, said tubular guide member having an opening formed therein adjacent the closed inner end thereof and in alignment with the angular bore portion of said off-set bore through said deflector block, and said inner and outer tubes being received in said tubular guide member with the inner ends thereof adjacent to said deflector block, the axially extending bore portion of said offset bore through said deflector block being in registration with the open inner end of said inner tube such that the detonation wave passing outwardly through the inner end of said inner tube continues through the offset bore in said deflector block and is discharged through the opening in said tubular guide member. 

1. In a rocket motor having a combustion chamber, a receptacle in said combustion chamber, an igniter assembly received by said receptacle, said igniter assembly including at least two spaced containing means one interior of the other, the interior one of said containing means being perforate and the exterior one thereof being imperforate, igniter charge means disposed between said spaced containing means, means dividing the interior one of said containing means into an inner end and an outer end, said inner end communicating with said combustion chamber, booster charge means received in said outer end, adaptor means enclosing said igniter assembly in said receptacle, said adaptor means including initiator charge means communicating with said booster charge means, and a squib for igniting said initiator charge means so that upon ignition said squib will, in order, cause initiation of said initiator charge means, said booster charge means, and said igniter charge means causing a detonation wave to pass through said inner end into said combustion chamber.
 2. In a rocket motor as defined in claim 1, wherein said receptacle includes deflector means attached to said inner end of the interior one of said containing means for selectively directing said detonation wave into said combustion chamber.
 3. In a rocket motor as defined in claim 1, wherein the strength of said interior dividing means may be varied, in conjunction with variation in the shape and amount of said booster charge means, to provide control of the initiation rate of said igniter charge means.
 4. An igniter assembly for rocket motors, said igniter assembly comprising inner and outer concentric elongated tubes disposed in radially spaced relation to each other to define an elongated longitudinally extending annular space therebetween, an igniter charge disposed in the annular Space between said inner and outer tubes, said inner tube having a plurality of apertures therethrough providing communication between the annular space and the interior of said inner tube, means defining a partition within said inner tube dividing the interior of said inner tube into inner and outer portions, a booster charge disposed in the outer portion of said inner tube, and means for initiating the ignition of said booster charge, and the ignition of said booster charge causing ignition of said igniter charge along the length of the annular space such that a detonation wave passes through apertures in said inner tube into the inner portion thereof and outwardly through the inner end of said inner tube.
 5. An igniter assembly as defined in claim 4, further including a tubular guide member having a closed inner end and provided with a deflector block received therein at the closed inner end thereof, said deflector block having an off-set bore extending therethrough which comprises an axially extending bore portion communicating with the interior of said tubular guide member and an angular bore portion extending radially outwardly from the axially extending bore portion, said tubular guide member having an opening formed therein adjacent the closed inner end thereof and in alignment with the angular bore portion of said off-set bore through said deflector block, and said inner and outer tubes being received in said tubular guide member with the inner ends thereof adjacent to said deflector block, the axially extending bore portion of said off-set bore through said deflector block being in registration with the open inner end of said inner tube such that the detonation wave passing outwardly through the inner end of said inner tube continues through the off-set bore in said deflector block and is discharged through the opening in said tubular guide member. 